How do I make my Minecraft server hardcore?

You make your Minecraft server hardcore by setting hardcore=true in server.properties. In hardcore the difficulty is locked to the hardest setting, and when you die you become a spectator: you can no longer play in that world.

Enable hardcore

1. Log in to the game panel, open your server and stop it with Stop.
2. Go to Files and open server.properties.
3. Find the line hardcore=false and change it to:

hardcore=true

4. Click Save Content.
5. For a new world, delete the world folders in Files. See How do I reset my Minecraft server's world?
6. Start your server with Start.

Check

Join your server. In hardcore your hearts look different, and you can no longer change the difficulty in the pause menu.

Let a player play again after dying

If a player has died and you want them back, type in the console:

gamemode survival <playername>

Turn hardcore off again

Change hardcore=true back to false and restart your server.